1. Field of the Invention
This invention relates to a system for monitoring and controlling the color and shade in a decoloration or fading process for textiles. More particularly, it relates to a novel system for use in quality control, color grading, shade sorting, color durability testing and the like within a washing machine during an oxidizing or reducing process of the dye on a garment or fabric.
2. Description of the Prior Art
Current fashion trends particularly with denim fabrics and garments dictate a faded and worn look in which the garment fabric becomes softened and more comfortable to wear. Denim is a stiff, durable, twilled fabric of cotton or cotton-blends woven with a colored warp and white filling threads. Usually the colored warp filaments have been dyed with indigo, i.e., a dark blue vat dye. To decolorize the garment and attain the fashionably faded look the garment or fabric is subjected to a process known in the textile art as stonewashing. Earlier prior art stonewashing methods such as disclosed in U.S. Pat. No. 4,575,887 issued to Viramontes involve treatment of denim with abrasives such as pumice stones. U.S. Pat. No. 4,997,450 issued to Olson, et al. gives an overview of these processes including the combination of abrasives and chemical bleaching agents.
In order to obtain the desired decoloration or fading of the denim fabric or garment, control of certain operating parameters are necessary. This is particularly the case with the more complex systems using bleaching agents. For example, the methods using chemical bleaching agents require more control of certain operating parameters, i.e., temperature, processing time, the nature and concentration of the bleaching agent, the nature of the fabric and dye, the pH of the treatment medium, as well as, the type of equipment, load volume, rate of process reaction and other variables.
In commercial stonewashing operations when it is intended that all garments undergo the same degree of decoloration or fading, exact color or shade matching must be reproducible from production run to production run and from plant location to plant location as well. The most common method for this color analysis is visual inspection which relies on the experience skilled operators. However, this method has no universality and is prone to personal errors of judgement resulting in costly inefficiencies and production losses. Under normal lighting conditions, the retina of the human eye has homogeneously distributed points which are primarily sensitive to different colors, i.e., red, green, and blue. The sensitivity to green is the greatest and the sensitivity to blue the least. The trained human eye has a capability of seeing a great number of colors and can discern differences in color shading. However, a difficulty with the human eye is that it cannot accurately determine two dissimilar shades within certain desirable limits due to its limited sensitivity. As mentioned above subjective and personal considerations also come into play.
Various apparatus are known for textile analysis. U.S. Pat. No. 3,999,860 issued to Demsky, et al discloses an apparatus which operates by measuring the reflectance at different wavelengths across the spectrum of visible light. The test sample is illuminated and the light reflected from the sample is detected. However, since the total light reflected includes both specular and diffuse components, and since the specular component gives rise to erroneous analysis these components must be separated. Spectrophotometer equipment is expensive, difficult to set-up and use in a plant environment. Moreover the instrument does not produce output results that are always consistent with the human eye.
Electronic optical image sensors and recorders mimic the function of the eye by sensing and recording an object or image using separate red, green and blue detectors. The optical image received by the optical sensor like in a color video camera for example is broken down to separate basic colors namely red, green and blue by specific optical devices (color separators) such as prisms. The detectors for each separate color may be arranged in a matrix dividing the image into a large number of small picture elements, pels or pixels. The signals from the detectors may be recombined and observed as a colored image, for example, on a cathode ray tube (TV monitor). The signals from the different color detectors may be processed and adjusted electronically so that in effect, the sensitivity of the red, green and blue can be varied. Furthermore, the sensitivities of the red, green and blue detectors may be varied relative to each other to electronically balance a perceived color of an object or image. The balancing of the perceived color provides the electronic image recorders and processors the capability of discerning color grading and shade sorting. However, none of this technology has been applied to monitor color and shade in the decolorization process of textile fabrics or garments.
Thus, the present invention provides a novel system for detecting the decolorization or fading of the fabric or garment, as well as, monitoring and controlling the decolorization process to achieve the desired color or shade.